TNF.alpha. (tumor necrosis factor alpha) binding at the plasma membrane induces intracellular signaling events that translate into the induction of NF-.kappa.B in the nucleus. The eukaryotic NF-.kappa.B/Rel (nuclear factor-.kappa.B/Rel) family of transcription factors plays an essential role in the regulation of inflammatory, immune, and apoptotic responses (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). One of the distinguishing characteristics of the NF-.kappa.B/Rel transcription factor is its post-translational regulation through interactions with cytoplasmic inhibitory proteins termed I.kappa.B (inhibitor-.kappa.B). NF-.kappa.B corresponds to an inducible eukaryotic transcription factor complex that is negatively regulated in resting cells, by its physical assembly with a family of cytoplasmic ankyrin-rich I.kappa.B inhibitors (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). Stimulation of cells with various pro-inflammatory cytokines, including TNF.alpha., induces nuclear NF-.kappa.B expression. The TNF.alpha.-signaling pathway is complex and involves recruitment of at least three adapter proteins, TRADD (TNF-R1 associated death domain protein) and TRAF-2 (TNF-receptor-associated factor)-2, and the serine/threonine kinase RIP (receptor interacting protein) to the cytoplasmic tail of the type 1 TNF receptor (Hsu et al Immunity 1996; Hsu et al Cell 1996) (FIG. 1). In turn, the recruitment of these factors promotes activation of the downstream NIK (Malinin et al 1997) and IKK.alpha. and IKK.beta. (I.kappa.B-specific kinases) (DiDonato et al 1997; Mercurio et al 1997; Regnier et al 1997; Woronicz et al 1997; Zandi et al 1997). The activated IKK.alpha. and IKK.beta. directly phosphorylates the two N-terminal regulatory serines within I.kappa.B.alpha., triggering ubiquitination and rapid degradation of this inhibitor in the 26S proteasome (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). Degradation of I.kappa.B.alpha. unmasks the nuclear localization signal on NF-.kappa.B, allowing the NF-.kappa.B to translocate to the nucleus where it engages cognate .kappa.B enhancer elements and activates the transcription of various .kappa.B-dependent genes involved in inflammatory, immune, and anti-apoptotic responses.
IL-1, a second proinflammatory cytokine, acts in a manner similar to TNF.alpha.. IL-1 binding to its receptor recruits the MyD88 and TRAF-6 adapter proteins and (IRAK), a serine-threonine kinase (Cao et al 1996; Muzio et al 1997). Like TRAF-2, TRAF-6 interacts with NIK. Thus, the TNF.alpha. and IL-1 signaling pathways converge at the level of NIK. The present invention provides new insights into the molecular basis for NIK regulation of NF-.kappa.B-dependent gene expression, and provides novel methods for modulating NF-.kappa.B-dependent immune, inflammatory, and anti-apoptotic responses.